Condensate accumulated in an engine exhaust during a prolonged vehicle key-off condition may cause erosion and rusting in exhaust system components such as in the tailpipe. For example, moisture from humid air may condense on engine components such as the exhaust passage and form a water puddle locally. Such water puddles may adversely affect operation of exhaust system sensors during subsequent engine operations.
Various approaches are provided for removing condensate from engine components. In one example approach shown in US 20140100074, Glugla et al. disclose a method to increase airflow through a charge air cooler (CAC) in order to purge condensate from the CAC. During an engine non-combusting condition, the transmission system is downshifted to a lower gear to increase engine speed and airflow via the CAC to purge stored condensate to the engine cylinders. By purging the condensate during an engine non-combusting condition, misfire events resulting from ingestion of water may be reduced.
However, the inventors herein have recognized potential disadvantages with the above approach. As one example, the approach may not be able to address condensate accumulated on one or more engine components such as the exhaust system. For example, during conditions when an engine is shutdown, such as during a vehicle key-off condition, or during hybrid vehicle propulsion using motor torque from a system battery, moisture from the ambient air may condense on and accumulate in the engine exhaust manifolds. During a drive cycle, due to engine start/stop conditions, deceleration fuel shut-off events, periods of vehicle propulsion using motor torque, the exhaust temperature may not be high enough to vaporize the moisture accumulated in the exhaust system. The moisture in the exhaust passage may increase the time required for an exhaust oxygen sensor to be functional, thereby causing the engine to operate under open loop control for a longer duration and emissions quality to be adversely affected. Further, freezing of water in the exhaust passage and/or water splashing on an exhaust oxygen sensor may result in inaccurate measurements made by the sensor which may adversely affect determination of air-fuel ratio and level of engine dilution desired during subsequent engine cycles.
The inventors herein have recognized that the issues described above may be addressed by an engine method comprising: responsive to each of a run-time of an engine of a vehicle during a drive cycle being below a threshold duration and a moisture level in either an exhaust system or an intake system of the engine being higher than a threshold level, at a key-off event following the drive cycle, activating an electric air compressor in the intake system to expel moisture from at least the exhaust system. In this way, when moisture accumulated in an engine exhaust system may be not be removed during an engine cycle, an electric air compressor may be operated during an immediately subsequent vehicle-off condition to flow compressed air through the engine exhaust system to remove any accumulated moisture.
As one example, during a vehicle key-off event, ambient humidity may be regularly monitored via on-board vehicle humidity sensors or via a remote server. On-board cameras may be used to monitor condensate formation on the vehicle windshield. Upon a vehicle key-on request, based on the ambient humidity conditions, local weather data, and images of the windshield, moisture formation in the engine exhaust system may be estimated. If the amount of moisture in the exhaust system is higher than a threshold, during the drive cycle, duration of engine operation may be estimated taking into account engine non-combusting conditions including engine start/stop conditions, decleration fuel shut-off event, and periods of vehicle propulsion using motor torque. Exhaust temperature may be monitored during the drive cycle. If the duration of engine operation is lower than a threshold, and/or if the exhaust temperature does not remain above a threshold temperature for a longer than threshold duration, it may be inferred that the exhaust heat may not be sufficient to vaporize the accumulated moisture. The engine may be a boosted engine comprising a turbine driven intake air compressor and an electrically driven intake air compressor (herein also referred to as a battery operated electric air compressor) that is selectively operated for providing additional boost during increased torque demand. During an immediately subsequent vehicle-off condition, the intake throttle may be opened, the exhaust gas recirculation (EGR) valve may be opened, and electric air compressor may be operated to flow compressed air through the engine exhaust system. The increased flow of compressed air through the engine components enables the accumulated moisture to be purged.
In this way, by selectively operating an electric air compressor, moisture accumulated in engine exhaust system may be effectively removed. The technical effect of operating the electric air compressor for moisture removal during a vehicle key-off condition is that by using an existing engine component for drying the engine exhaust system, the need for additional components for condensate removal is eliminated. By removing moisture from the exhaust manifold, heating of oxygen sensors may be expedited and closed loop control of engine fueling may be initiated earlier, improving fuel economy and emissions quality. Overall, by timely purging water accumulated in the engine exhaust system, engine system components may be protected from degradation and exhaust system sensors may be optimally operated during subsequent engine cycles.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.